Adductor spasmodic dysphonia causes erratic, involuntary adduction spasms of both vocal cords. As the patient strains to speak through the narrowed vocal tract, the voice takes on a high-pitched, strained, choked quality that varies markedly during the course of a sentence. The much rarer abductor spasmodic dysphonia is due to spasmodic contraction of the posterior cricoarytenoid, which causes a failure of normal adduction on phonation; the voice is breathy and hoarse. In both types, there is often a dramatic improvement in the voice during shouting, whispering, or singing. Direct and indirect laryngoscopy and videostroboscopy are valuable adjuncts to the routine examination. Both types may respond dramatically to the injection of botulinum toxin into the involved muscle.
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